DES MOINES — Senator Bernie Sanders of Vermont raised more than $34.5 million in the fourth quarter of 2019, his presidential campaign said Thursday, yet another display of his enduring financial might fueled by a huge base of grass-roots donors.
Mr. Sanders received more than 1.8 million donations in the quarter, with an average donation of $18.53.
His fourth-quarter total is larger than any candidate has raised in a single quarter so far in the primary race. And it soundly eclipsed the totals of several other candidates who have reported figures for the three-month period from Oct. 1 until Dec. 31, including Pete Buttigieg, who said on Wednesday that he had raised more than $24.7 million; Joseph R. Biden Jr., who said on Thursday that he had collected $22.7 million; and Andrew Yang, who said on Thursday that he had raised more than $16.5 million.
Taken together, the high totals suggest the willingness of Democrats eager to defeat President Trump to open their checkbooks and donate to potential nominees.
But Mr. Trump still retains a formidable fund-raising advantage: On Thursday, his re-election campaign said it had raised $46 million in the final quarter of 2019. That total does not include funds raised by the Republican National Committee.
The Trump campaign said it had raised $143 million in 2019 and had a staggering $102.7 million in cash on hand.
Mr. Sanders revealed his fund-raising haul a day after announcing that he had received more than five million donations since entering the race, which he said was more “than any campaign has received at this point in a presidential election in the history of our country.”
Mr. Sanders has raised more than $96 million since he announced he was running for president last February, his campaign said.
His fund-raising success underscores why Mr. Sanders remains such a formidable candidate in the race: Despite having a heart attack that threatened to derail his bid in early October, he retains loyal supporters who are faithful to him — and undaunted by his setbacks — in a way that no other candidates’ supporters are.
That devotion did not just help revive Mr. Sanders’s campaign; it has buttressed his fund-raising prowess and kept him a front-runner, in Iowa and elsewhere. Now, with less than five weeks until the caucuses here, even Democratic officials acknowledge he is being underestimated.
His campaign has already earmarked tens of millions of dollars for television advertising in the first four nominating states and California — a tangible benefit of being so flush with cash. He can also begin to advertise and build organizational strength in other Super Tuesday states, an advantage few of his rivals can match.
And the huge influx of money gives him the resources to persist well into the primary season, unless he completely flops with voters in early states.
Another leading candidate, Senator Elizabeth Warren of Massachusetts, has not yet disclosed her fund-raising total.
In a statement, Faiz Shakir, Mr. Sanders’s campaign manager, said Mr. Sanders “is proving each and every day that working class Americans are ready and willing to fully fund a campaign that stands up for them and takes on the biggest corporations and the wealthy.”
He added: “You build a grass-roots movement to beat Donald Trump and create a political revolution one $18 donation at a time, and that’s exactly why Bernie is going to win.”
Mr. Sanders’s campaign said he had raised more than $18 million, from more than 900,000 donations, just in the month of December. It also said it had received contributions from more than 40,000 new donors on the last day of the year.
The total for the fourth quarter easily surpassed what he raised in the third quarter, $25.3 million. That total — which he announced hours before he began to experience chest pains at a campaign event in Las Vegas — was the largest in the Democratic field, narrowly exceeding the total raised by Ms. Warren, who is also relying on small donations.
While Ms. Warren’s campaign has acknowledged that its fund-raising slipped in the fourth quarter, Mr. Sanders’s accelerated.
His total for the fourth quarter showed the continuing strength of his grass-roots fund-raising base, a significant advantage for him, especially if the primary race turns out to be a lengthy one. Supporters who give him small amounts can continue to donate over and over, unlike big donors, many of whom give the maximum contribution of $2,800 for the primary race.
His campaign said 99.99 percent of donors had not maxed out.
Sydney Ember reported from Des Moines, and Thomas Kaplan from Washington.